Audio signal processing apparatus

ABSTRACT

In an audio signal encoding apparatus, a first audio signal and a second audio signal are added into an addition-result signal. The first audio signal is subtracted from the second audio signal to generate a subtraction-result signal. A first difference signal is generated which represents a difference in the addition-result signal. A second difference signal is generated which represents a difference in the subtraction-result signal. A plurality of first predictors have different prediction characteristics respectively, and are responsive to the first difference signal for generating first different prediction signals for the first difference signal, respectively. A plurality of first subtracters operate for generating first prediction-error signals representing differences between the first difference signal and the first different prediction signals, respectively. A first minimum prediction-error signal representative of a smallest difference is selected from among the first prediction-error signals. A plurality of second predictors have different prediction characteristics respectively, and are responsive to the second difference signal for generating second different prediction signals for the second difference signal, respectively. A plurality of second subtracters operate for generating second prediction-error signals representing differences between the second difference signal and the second different prediction signals, respectively. A second minimum prediction-error signal representative of a smallest difference is selected from among the second prediction-error signals.

RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.10/096,276, filed Mar. 13, 2002 now U.S. Pat. No. 6,678,652 which inturn is a divisional of U.S. application Ser. No. 09/394,688, filed Sep.13, 1999 now U.S. Pat. No. 6,463,410.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an audio signal encoding apparatus. Thisinvention also relates to an optical recording medium. In addition, thisinvention relates to an audio signal decoding apparatus. Furthermore,this invention relates to a method of transmitting an audio signal.

2. Description of the Related Art

Highly efficient encoding of an audio signal includes a step ofcompressing the audio signal. Highly efficient encoding techniques areclassified into two types; the lossy encoding techniques and thelossless encoding techniques. Among the lossy encoding techniques, the“acoustic encoding” is well known as a technique which renders the datadeterioration acoustically undetectable. On the other hand, according tothe lossless encoding and decoding techniques, the recovered data areexactly the same as the original data.

In general, a sampled or uniformly quantized audio signal hassignificant redundancy. During the encoding of such an audio signal, thedegree of the compression of the audio signal rises as redundancy ismore effectively removed therefrom,

SUMMARY OF THE INVENTION

It is a first object of this invention to provide an audio signalencoding apparatus having a higher compression performance.

It is a second object of this invention to provide an improved opticalrecording medium.

It is a third object of this invention to provide an improved audiosignal decoding apparatus.

It is a fourth object of this invention to provide an improved method oftransmitting an audio signal.

A first aspect of this invention provides an audio signal encodingapparatus comprising means for adding a first audio signal and a secondaudio signal into an addition-result signal; means for subtracting thefirst audio signal from the second audio signal, and generating asubtraction-result signal; means responsive to the addition-resultsignal for generating a first difference signal representing adifference in the addition-result signal; means responsive to thesubtraction-result signal for generating a second difference signalrepresenting a difference in the subtraction-result signal; a pluralityof first predictors having different prediction characteristicsrespectively and being responsive to the first difference signal forgenerating first different prediction signals for the first differencesignal, respectively; a plurality of first subtracters for generatingfirst prediction-error signals representing differences between thefirst difference signal and the first different prediction signals,respectively; means for selecting a first minimum prediction-errorsignal representative of a smallest difference from among the firstprediction-error signals; a plurality of second predictors havingdifferent prediction characteristics respectively and being responsiveto the second difference signal for generating second differentprediction signals for the second difference signal, respectively; aplurality of second subtracters for generating second prediction-errorsignals representing differences between the second difference signaland the second different prediction signals, respectively; and means forselecting a second minimum prediction-error signal representative of asmallest difference from among the second prediction-error signals.

A second aspect of this invention is based on the first aspect thereof,and provides an audio signal encoding apparatus further comprising meansfor generating a variable-rate bit stream in response to the firstminimum prediction-error signal and the second minimum prediction-errorsignal.

A third aspect of this invention provides an audio signal decodingapparatus for processing a first minimum prediction-error signal and asecond minimum prediction-error signal which are generated by an audiosignal encoding apparatus comprising means for adding a first audiosignal and a second audio signal into an addition-result signal; meansfor subtracting the first audio signal from the second audio signal, andgenerating a subtraction-result signal; means responsive to theaddition-result signal for generating a first difference signalrepresenting a difference in the addition-result signal; meansresponsive to the subtraction-result signal for generating a seconddifference signal representing a difference in the subtraction-resultsignal; a plurality of first predictors having different predictioncharacteristics respectively and being responsive to the firstdifference signal for generating first different prediction signals forthe first difference signal, respectively; a plurality of firstsubtracters for generating first prediction-error signals representingdifferences between the first difference signal and the first differentprediction signals, respectively; means for selecting a first minimumprediction-error signal representative of a smallest difference fromamong the first prediction-error signals; a plurality of secondpredictors having different prediction characteristics respectively andbeing responsive to the second difference signal for generating seconddifferent prediction signals for the second difference signal,respectively; a plurality of second subtracters for generating secondprediction-error signals representing differences between the seconddifference signal and the second different prediction signals,respectively; and means for selecting a second minimum prediction-errorsignal representative of a smallest difference from among the secondprediction-error signals. The audio signal decoding apparatus comprisesmeans for recovering the addition-result signal from the first minimumprediction-error signal; means for recovering the subtraction-resultsignal from the second minimum prediction-error signal; and means forrecovering the first audio signal and the second audio signal from therecovered addition-result signal and the recovered subtraction-resultsignal.

A fourth aspect of this invention provides a method comprising the stepsof adding a first audio signal and a second audio signal into anaddition-result signal; subtracting the first audio signal from thesecond audio signal, and generating a subtraction-result signal;generating a first difference signal representing a difference in theaddition-result signal; generating a second difference signalrepresenting a difference in the subtraction-result signal; generatingfirst different prediction signals for the first difference signal,respectively; generating first prediction-error signals representingdifferences between the first difference signal and the first differentprediction signals, respectively; selecting a first minimumprediction-error signal representative of a smallest difference fromamong the first prediction-error signals; generating second differentprediction signals for the second difference signal, respectively;generating second prediction-error signals representing differencesbetween the second difference signal and the second different predictionsignals, respectively; selecting a second minimum prediction-errorsignal representative of a smallest difference from among the secondprediction-error signals; and transmitting the first minimumprediction-error signal and the second minimum prediction-error signalto a communication line.

A fifth aspect of this invention provides an optical recording mediumstoring formatted information of a first minimum prediction-error signaland a second minimum prediction-error signal which are generated by anaudio signal encoding apparatus comprising means for adding a firstaudio signal and a second audio signal into an addition-result signal;means for subtracting the first audio signal from the second audiosignal, and generating a subtraction-result signal; means responsive tothe addition-result signal for generating a first difference signalrepresenting a difference in the addition-result signal; meansresponsive to the subtraction-result signal for generating a seconddifference signal representing a difference in the subtraction-resultsignal; a plurality of first predictors having different predictioncharacteristics respectively and being responsive to the firstdifference signal for generating first different prediction signals forthe first difference signal, respectively; a plurality of firstsubtracters for generating first prediction-error signals representingdifferences between the first difference signal and the first differentprediction signals, respectively; means for selecting a first minimumprediction-error signal representative of a smallest difference fromamong the first prediction-error signals; a plurality of secondpredictors having different prediction characteristics respectively andbeing responsive to the second difference signal for generating seconddifferent prediction signals for the second difference signal,respectively; a plurality of second subtracters for generating secondprediction-error signals representing differences between the seconddifference signal and the second different prediction signals,respectively; and means for selecting a second minimum prediction-errorsignal representative of a smallest difference from among the secondprediction-error signals.

A sixth aspect of this invention provides a method of network-basedtransmission which comprises the steps of adding a first audio signaland a second audio signal into an addition-result signal; subtractingthe first audio signal from the second audio signal, and generating asubtraction-result signal; generating a first difference signalrepresenting a difference in the addition-result signal; generating asecond difference signal representing a difference in thesubtraction-result signal; generating first different prediction signalsfor the first difference signal, respectively; generating firstprediction-error signals representing differences between the firstdifference signal and the first different prediction signals,respectively; selecting a first minimum prediction-error signalrepresentative of a smallest difference from among the firstprediction-error signals; generating second different prediction signalsfor the second difference signal, respectively; generating secondprediction-error signals representing differences between the seconddifference signal and the second different prediction signals,respectively; selecting a second minimum prediction-error signalrepresentative of a smallest difference from among the secondprediction-error signals; and transmitting the first minimumprediction-error signal and the second minimum prediction-error signalto a communication line.

A seventh aspect of this invention provides an audio signal encodingapparatus comprising means for selecting a first audio signal and asecond audio signal from among signals composing a multi-channel audiosignal; means for adding the first audio signal and the second audiosignal into an addition-result signal; means for subtracting the firstaudio signal from the second audio signal, and generating asubtraction-result signal; means responsive to the addition-resultsignal for generating a first difference signal representing adifference in the addition-result signal; means responsive to thesubtraction-result signal for generating a second difference signalrepresenting a difference in the subtraction-result signal; a pluralityof first predictors having different prediction characteristicsrespectively and being responsive to the first difference signal forgenerating first different prediction signals for the first differencesignal, respectively; a plurality of first subtracters for generatingfirst prediction-error signals representing differences between thefirst difference signal and the first different prediction signals,respectively; means for selecting a first minimum prediction-errorsignal representative of a smallest difference from among the firstprediction-error signals; a plurality of second predictors havingdifferent prediction characteristics respectively and being responsiveto the second difference signal for generating second differentprediction signals for the second difference signal, respectively; aplurality of second subtracters for generating second prediction-errorsignals representing differences between the second difference signaland the second different prediction signals, respectively; and means forselecting a second minimum prediction-error signal representative of asmallest difference from among the second prediction-error signals.

An eighth aspect of this invention is based on the seventh aspectthereof, and provides an audio signal encoding apparatus furthercomprising means for generating a variable-rate bit stream in responseto the first minimum prediction-error signal and the second minimumprediction-error signal.

A ninth aspect of this invention provides an audio signal decodingapparatus for processing a first minimum prediction-error signal and asecond minimum prediction-error signal which are generated by an audiosignal encoding apparatus comprising means for selecting a first audiosignal and a second audio signal from among signals composing amulti-channel audio signal; means for adding the first audio signal andthe second audio signal into an addition-result signal; means forsubtracting the first audio signal from the second audio signal, andgenerating a subtraction-result signal; means responsive to theaddition-result signal for generating a first difference signalrepresenting a difference in the addition-result signal; meansresponsive to the subtraction-result signal for generating a seconddifference signal representing a difference in the subtraction-resultsignal; a plurality of first predictors having different predictioncharacteristics respectively and being responsive to the firstdifference signal for generating first different prediction signals forthe first difference signal, respectively; a plurality of firstsubtracters for generating first prediction-error signals representingdifferences between the first difference signal and the first differentprediction signals, respectively; means for selecting a first minimumprediction-error signal representative of a smallest difference fromamong the first prediction-error signals; a plurality of secondpredictors having different prediction characteristics respectively andbeing responsive to the second difference signal for generating seconddifferent prediction signals for the second difference signal,respectively; a plurality of second subtracters for generating secondprediction-error signals representing differences between the seconddifference signal and the second different prediction signals,respectively; and means for selecting a second minimum prediction-errorsignal representative of a smallest difference from among the secondprediction-error signals. The audio signal decoding apparatus comprisesmeans for recovering the addition-result signal from the first minimumprediction-error signal; means for recovering the subtraction-resultsignal from the second minimum prediction-error signal; and means forrecovering the first audio signal and the second audio signal from therecovered addition-result signal and the recovered subtraction-resultsignal.

A tenth aspect of this invention provides a method comprising the stepsof selecting a first audio signal and a second audio signal from amongsignals composing a multi-channel audio signal; adding the first audiosignal and the second audio signal into an addition-result signal;subtracting the first audio signal from the second audio signal, andgenerating a subtraction-result signal; generating a first differencesignal representing a difference in the addition-result signal;generating a second difference signal representing a difference in thesubtraction-result signal; generating first different prediction signalsfor the first difference signal, respectively; generating firstprediction-error signals representing differences between the firstdifference signal and the first different prediction signals,respectively; selecting a first minimum prediction-error signalrepresentative of a smallest difference from among the firstprediction-error signals; generating second different prediction signalsfor the second difference signal, respectively; generating secondprediction-error signals representing differences between the seconddifference signal and the second different prediction signals,respectively; selecting a second minimum prediction-error signalrepresentative of a smallest difference from among the secondprediction-error signals; and transmitting the first minimumprediction-error signal and the second minimum prediction-error signalto a communication line.

An eleventh aspect of this invention provides an optical recordingmedium storing formatted information of a first minimum prediction-errorsignal and a second minimum prediction-error signal which are generatedby an audio signal encoding apparatus comprising means for selecting afirst audio signal and a second audio signal from among signalscomposing a multi-channel audio signal; means for adding the first audiosignal and the second audio signal into an addition-result signal; meansfor subtracting the first audio signal from the second audio signal, andgenerating a subtraction-result signal; means responsive to theaddition-result signal for generating a first difference signalrepresenting a difference in the addition-result signal; meansresponsive to the subtraction-result signal for generating a seconddifference signal representing a difference in the subtraction-resultsignal; a plurality of first predictors having different predictioncharacteristics respectively and being responsive to the firstdifference signal for generating first different prediction signals forthe first difference signal, respectively; a plurality of firstsubtracters for generating first prediction-error signals representingdifferences between the first difference signal and the first differentprediction signals, respectively; means for selecting a first minimumprediction-error signal representative of a smallest difference fromamong the first prediction-error signals; a plurality of secondpredictors having different prediction characteristics respectively andbeing responsive to the second difference signal for generating seconddifferent prediction signals for the second difference signal,respectively; a plurality of second subtracters for generating secondprediction-error signals representing differences between the seconddifference signal and the second different prediction signals,respectively; and means for selecting a second minimum prediction-errorsignal representative of a smallest difference from among the secondprediction-error signals.

A twelfth aspect of this invention provides a method of network-basedtransmission which comprises the steps of selecting a first audio signaland a second audio signal from among signals composing a multi-channelaudio signal; adding the first audio signal and the second audio signalinto an addition-result signal; subtracting the first audio signal fromthe second audio signal, and generating a subtraction-result signal;generating a first difference signal representing a difference in theaddition-result signal; generating a second difference signalrepresenting a difference in the subtraction-result signal; generatingfirst different prediction signals for the first difference signal,respectively; generating first prediction-error signals representingdifferences between the first difference signal and the first differentprediction signals, respectively; selecting a first minimumprediction-error signal representative of a smallest difference fromamong the first prediction-error signals; generating second differentprediction signals for the second difference signal, respectively;generating second prediction-error signals representing differencesbetween the second difference signal and the second different predictionsignals, respectively; selecting a second minimum prediction-errorsignal representative of a smallest difference from among the secondprediction-error signals; and transmitting the first minimumprediction-error signal and the second minimum prediction-error signalto a communication line.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a system including an audio signal encodingapparatus and an audio signal decoding apparatus according to a firstembodiment of this invention.

FIG. 2 is a block diagram of a lossless encoder in FIG. 1.

FIG. 3 is a diagram of the format of a 1-frame-corresponding segment ofa variable-rate bit stream generated by the audio signal encodingapparatus in FIG. 1.

FIG. 4 is a block diagram of a lossless decoder in FIG. 1.

FIG. 5 is a block diagram of a lossless encoder in a second embodimentof this invention.

FIG. 6 is a block diagram of a lossless decoder in the second embodimentof this invention.

FIG. 7 is a block diagram of an audio signal encoding apparatus in athird embodiment of this invention.

FIG. 8 is a block diagram of an audio signal decoding apparatus in thethird embodiment of this invention.

FIG. 9 is a block diagram of a system according to a fourth embodimentof this invention.

FIG. 10 is a diagram of the structure of an audio pack.

FIG. 11 is a diagram of the structure of the audio pack.

FIG. 12 is a block diagram of a system according to a fifth embodimentof this invention.

FIG. 13 is a flowchart of a segment of a control program for a packetingprocessor in FIG. 12.

FIG. 14 is a flowchart of a segment of a control program for ade-packeting processor in FIG. 12.

FIG. 15 is a block diagram of a system including an audio signalencoding apparatus and an audio signal decoding apparatus according to asixth embodiment of this invention.

FIG. 16 is a diagram of the format of a 1-frame-corresponding segment ofa variable-rate bit stream generated in the system of FIG. 15.

FIG. 17 is a block diagram of a system including an audio signalencoding apparatus and an audio signal decoding apparatus according to aseventh embodiment of this invention.

FIG. 18 is a diagram of the format of a 1-frame-corresponding segment ofa variable-rate bit stream generated in the system of FIG. 17.

FIG. 19 is a block diagram of a system including an audio signalencoding apparatus and an audio signal decoding apparatus according toan eighth embodiment of this invention.

FIG. 20 is a block diagram of a system including an audio signalencoding apparatus and an audio signal decoding apparatus according to aninth embodiment of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIRST EMBODIMENT

With reference to FIG. 1, an audio signal encoding apparatus 100includes a channel correlation circuit “A” and a lossless encoder 2D. Anaudio signal decoding apparatus 200 includes a channel correlationcircuit “B” and a lossless decoder 3D. The audio signal encodingapparatus 100 and the audio signal decoding apparatus 200 are connectedvia a transmission line 250.

The audio signal encoding apparatus 100 receives stereophonic 2-channeldigital audio signals, that is, a left-channel digital audio signal “L”and a right-channel digital audio signal “R”. The stereophonic 2-channeldigital audio signals are reproduced from a digital recording mediumsuch as a DVD-audio (a digital versatile disc audio). The audio signalencoding apparatus 100 encodes the left-channel digital audio signal “L”and the right-channel digital audio signal “R” into encoding-resultantdigital audio signals. The audio signal encoding apparatus 100 outputsthe encoding-resultant digital audio signals to the transmission line250. The encoding-resultant digital audio signals are propagated to theaudio signal decoding apparatus 200 via the transmission line 250. Theaudio signal decoding apparatus 200 decodes the encoding-resultantdigital audio signals into the original left-channel digital audiosignal “L” and the original right-channel digital audio signal “R”. Inother words, the audio signal decoding apparatus 200 recovers theoriginal left-channel digital audio signal “L” and the originalright-channel digital audio signal “R”. The audio signal decodingapparatus 200 outputs the recovered left-channel digital audio signal“L” and the recovered right-channel digital audio signal “R” to anexternal apparatus.

The channel correlation circuit “A” in the audio signal encodingapparatus 100 includes an addition circuit 1 a and a subtraction circuit1 b. The addition circuit 1 a receives the left-channel digital audiosignal “L” and the right-channel digital audio signal “R”. Theleft-channel digital audio signal “L” results from quantization of aleft-channel analog audio signal at a predetermined sampling frequencyand a predetermined quantization bit number. The predetermined samplingfrequency is equal to, for example, 192 kHz. The predeterminedquantization bit number is equal to, for example, 24. Similarly, theright-channel digital audio signal “R” results from quantization of aright-channel analog audio signal at the predetermined samplingfrequency and the predetermined quantization bit number. The additioncircuit 1 a adds the left-channel digital audio signal “L” and theright-channel digital audio signal “R” into an addition-result signal(L+R). The addition-result signal (L+R) is a PCM (pulse code modulation)signal. The addition circuit 1 a outputs the addition-result signal(L+R) to the lossless encoder 2D. The subtraction circuit 1 b receivesthe left-channel digital audio signal “L” and the right-channel digitalaudio signal “R”.

The subtraction circuit 1 b subtracts the right-channel digital audiosignal “R” from the left-channel digital audio signal “L”, therebygenerating a subtraction-result signal (L−R). The subtraction-resultsignal (L−R) is a PCM signal. The subtraction circuit 1 b outputs thesubtraction-result signal (L−R) to the lossless encoder 2D.

As shown in FIG. 2, the lossless encoder 2D includes a buffer (a memory)10. A sequence of samples of the addition-result signal (L+R) and asequence of samples of the subtraction-result signal (L−R) are appliedto the buffer 10. The addition-result signal (L+R) and thesubtraction-result signal (L−R) are stored into the buffer 10 frame byframe. Every frame is composed of a predetermined number of successivesamples.

Samples of the addition-result signal (L+R) are sequentially transmittedfrom the buffer 10 to a difference calculation circuit 11D1. Thedifference calculation circuit 11D1 generates a signal Δ(L+R)representing the difference between the current sample of theaddition-result signal (L+R) and the immediately preceding samplethereof. The difference calculation circuit 11D1 outputs the differencesignal Δ(L+R) to a prediction circuit 15D1 sample by sample. In otherwords, the differential calculation circuit 11D1 implements differentialpulse code modulation (DPCM) of the addition-result signal (L+R), andoutputs the resultant DPCM signal Δ(L+R).

Samples of the subtraction-result signal (L−R) are sequentiallytransmitted from the buffer 10 to a difference calculation circuit 11D2.The difference calculation circuit 11D2 generates a signal Δ(L−R)representing the difference between the current sample of thesubtraction-result signal (L−R) and the immediately preceding samplethereof. The difference calculation circuit 11D2 outputs the differencesignal Δ(L−R) to a prediction circuit 15D2 sample by sample. In otherwords, the differential calculation circuit 11D2 implements differentialpulse code modulation (DPCM) of the subtraction-result signal (L−R), andoutputs the resultant DPCM signal Δ(L−R).

For every frame, the first sample of the addition-result signal (L+R)and the first sample of the subtraction-result signal (L−R) aretransmitted from the buffer 10 to a multiplexer 19.

The prediction circuit 15D1 includes predictors 12 a-1, 12 a-2, . . . ,and 12 a-n, and subtracters 13 a-1, 13 a-2, . . . , and 13 a-n, where“n” denotes a predetermined natural number equal to or greater than 2.The predictors 12 a-1, 12 a-2, . . . , and 12 a-n receive every sampleof the difference signal Δ(L+R) from the difference calculation circuit11D1. Also, the subtracters 13 a-1, 13 a-2, . . . , and 13 a-n receiveevery sample of the difference signal Δ(L+R) from the differencecalculation circuit 11D1. The predictors 12 a-1, 12 a-2, . . . , and 12a-n have different prediction characteristics, respectively.Specifically, the predictors 12 a-1, 12 a-2, . . . , and 12 a-n aredifferent from each other in prediction coefficients. Each of thepredictors 12 a-1, 12 a-2, . . . , and 12 a-n predicts a current sampleof the difference signal Δ(L+R) from preceding samples thereof inresponse to the related prediction coefficients. Thus, the predictors 12a-1, 12 a-2, . . . , and 12 a-n generate prediction-result signals forthe difference signal Δ(L+R) in response to the prediction coefficients,respectively. The predictors 12 a-1, 12 a-2, . . . , and 12 a-n outputthe prediction-result signals to the subtracters 13 a-1, 13 a-2, . . . ,and 13 a-n respectively. For every sample, each of the subtracters 13a-1, 13 a-2, . . . , and 13 a-n subtracts the related prediction-resultsignal from the difference signal Δ(L+R), and hence generates a signalrepresenting the prediction error between the prediction-result signaland the difference signal Δ(L+R). The subtracters 13 a-1, 13 a-2, . . ., and 13 a-n output the respective prediction-error signals to a bufferand selector 16D1.

The prediction-error signals, that is, the output signals of thesubtracters 13 a-1, 13 a-2, . . . , and 13 a-n, are temporarily storedin a memory within the buffer and selector 16D1. A selection signalgenerator 17 produces a first selection signal. The selection signalgenerator 17 outputs the first selection signal to the buffer andselector 16D1. The first selection signal is designed to select thesmallest one from among the prediction-error signals in the memory ofthe buffer and selector 16D1 as an output signal of an optimumsubtracter (an optimum predictor) for every sub-frame. Specifically, forevery sub-frame, the selection signal generator 17 searches the memorywithin the buffer and selector 16D1 for the smallest prediction-errorsignal. In more detail, for every sub-frame, the sums of the valuesrepresented by samples of the respective prediction-error signals arecalculated. The calculated sums are compared to determine the smallestone which corresponds to the smallest prediction-error signal to beselected. The selection signal generator 17 enables the buffer andselector 16D1 to output the smallest prediction-error signal from thememory to a packing circuit 18 as the selected (L+R)-relatedprediction-error signal for every sub-frame.

Every sub-frame is composed of a predetermined number of successivesamples. Several tens of successive sub-frames compose one frame. Forexample, 80 successive sub-frames compose one frame.

The prediction circuit 15D2 includes predictors 12 b-1, 12 b-2, . . . ,and 12 b-n, and subtracters 13 b-1, 13 b-2, . . . , and 13 b-n. Thepredictors 12 b-1, 12 b-2, . . . , and 12 b-n receive every sample ofthe difference signal Δ(L−R) from the difference calculation circuit11D2. Also, the subtracters 13 b-1, 13 b-2, . . . , and 13 b-n receiveevery sample of the difference signal Δ(L−R) from the differencecalculation circuit 11D2. The predictors 12 b-1, 12 b-2, . . . , and 12b-n have different prediction characteristics, respectively.Specifically, the predictors 12 b-1, 12 b-2, . . . , and 12 b-n aredifferent from each other in prediction coefficients. Each of thepredictors 12 b-1, 12 b-2, . . . , and 12 b-n predicts a current sampleof the difference signal Δ(L−R) from preceding samples thereof inresponse to the related prediction coefficients. Thus, the predictors 12b-1, 12 b-2, . . . , and 12 b-n generate prediction-result signals forthe difference signal Δ(L−R) in response to the prediction coefficients,respectively. The predictors 12 b-1, 12 b-2, . . . , and 12 b-n outputthe prediction-result signals to the subtracters 13 b-1, 13 b-2, . . . ,and 13 b-n respectively. For every sample, each of the subtracters 13b-1, 13 b-2, . . . , and 13 b-n subtracts the related prediction-resultsignal from the difference signal Δ(L−R), and hence generates a signalrepresenting the prediction error between the prediction-result signaland the difference signal Δ(L−R). The subtracters 13 b-1, 13 b-2, . . ., and 13 b-n output the respective prediction-error signals to a bufferand selector 16D2.

The prediction-error signals, that is, the output signals of thesubtracters 13 b-1, 13 b-2, . . . , and 13 b-n, are temporarily storedin a memory within the buffer and selector 16D2. The selection signalgenerator 17 produces a second selection signal. The selection signalgenerator 17 outputs the second selection signal to the buffer andselector 16D2. The second selection signal is designed to select thesmallest one from among the prediction-error signals in the memory ofthe buffer and selector 16D2 as an output signal of an optimumsubtracter (an optimum predictor) for every sub-frame.

Specifically, for every sub-frame, the selection signal generator 17searches the memory within the buffer and selector 16D2 for the smallestprediction-error signal. In more detail, for every sub-frame, the sumsof the values represented by samples of the respective prediction-errorsignals are calculated. The calculated sums are compared to determinethe smallest one which corresponds to the smallest prediction-errorsignal to be selected. The selection signal generator 17 enables thebuffer and selector 16D1 to output the smallest prediction-error signalfrom the memory to the packing circuit 18 as the selected (L−R)-relatedprediction-error signal for every sub-frame.

In addition, the selection signal generator 17 produces a first flag,for example, a first 5-bit flag representing the maximum number amongthe numbers of effective bits in respective samples of the selected(L+R)-related prediction-error signal which compose one sub-frame. Forevery sub-frame, the selection signal generator 17 outputs the firstflag to the packing circuit 18 and the multiplexer 19 as an(L+R)-related bit-number flag.

Similarly, the selection signal generator 17 produces a second flag, forexample, a second 5-bit flag representing the maximum number among thenumbers of effective bits in respective samples of the selected(L−R)-related prediction-error signal which compose one sub-frame. Forevery sub-frame, the selection signal generator 17 outputs the secondflag to the packing circuit 18 and the multiplexer 19 as an(L−R)-related bit-number flag.

Numerals “1”, “2”, . . . , and “n” are assigned to the predictors 12a-1, 12 a-2, . . . , and 12 a-n (or the subtracters 13 a-1, 13 a-2, . .. , and 13 a-n) as identification numbers therefor, respectively. Forevery sub-frame, the selection signal generator 17 produces a third flagrepresenting the optimal predictor among the predictors 12 a-1, 12 a-2,. . . , and 12 a-n, that is, the predictor causing the selected(L+R)-related prediction-error signal. When the predetermined number “n”is equal to 9, the third flag has 3 bits. The selection signal generator17 outputs the third flag to the multiplexer 19 as an (L+R)-relatedpredictor-selection flag.

Similarly, numerals “1”, “2”, . . . , and “n” are assigned to thepredictors 12 b-1, 12 b-2, . . . , and 12 b-n (or the subtracters 13b-1, 13 b-2, . . . , and 13 b-n) as identification numbers therefor,respectively. For every sub-frame, the selection signal generator 17produces a fourth flag representing the optimal predictor among thepredictors 12 a-1, 12 a-2, . . . , and 12 a-n, that is, the predictorcausing the selected (L−R)-related prediction-error signal. When thepredetermined number “n” is equal to 9, the fourth flag has 3 bits. Theselection signal generator 17 outputs the fourth flag to the multiplexer19 as an (L−R)-related predictor-selection flag.

For every sub-frame, the packing circuit 18 packs each of samples of theselected (L+R)-related prediction-error signal into bits, the number ofwhich is equal to the maximum bit number represented by the(L+R)-related bit-number flag. The packing circuit 18 outputs everypacking-resultant sample of the selected (L+R)-related prediction-errorsignal to the multiplexer 19. In addition, for every sub-frame, thepacking circuit 18 packs each of samples of the selected (L−R)-relatedprediction-error signal into bits, the number of which is equal to themaximum bit number represented by the (L−R)-related bit-number flag. Thepacking circuit 18 outputs every packing-resultant sample of theselected (L−R)-related prediction-error signal to the multiplexer 19.

A signal generator 20 periodically produces a signal representing apredetermined frame header having, for example, 40 bits. The signalgenerator 20 outputs the frame-header signal to the multiplexer 19.

The multiplexer 19 receives the frame-header signal from the signalgenerator 20 for every frame. The multiplexer 19 receives the firstsample of the addition-result signal (L+R) and the first sample of thesubtraction-result signal (L−R) from the buffer 10 for every frame. Themultiplexer 19 receives the (L+R)-related predictor-selection flag andthe (L−R)-related predictor-selection flag from the selection signalgenerator 17 for every sub-frame. The multiplexer 19 receives the(L+R)-related bit-number flag and the (L−R)-related bit-number flag fromthe selection signal generator 17 for every sub-frame. The multiplexer19 receives every packing-resultant sample of the selected (L+R)-relatedprediction-error signal and every packing-resultant sample of theselected (L−R)-related prediction-error signal from the packing circuit18. The multiplexer 19 multiplexes the received signals and flags into avariable-rate bit stream on a time sharing basis. The multiplexer 19outputs the variable-rate bit stream to the transmission line 250 (seeFIG. 1). The variable-rate bit stream represents a sequence ofvariable-bit-number frames.

FIG. 3 shows the format of every frame of the variable-rate bit streamoutputted from the multiplexer 19. As shown in FIG. 3, a startingportion of every frame has the 40-bit frame header. The 40-bit frameheader is successively followed by the 25-bit first sample of theaddition-result signal (L+R), the 25-bit first sample of thesubtraction-result signal (L−R), a set of the 80 (L+R)-relatedpredictor-selection flags each having 3 bits, a set of the 80(L−R)-related predictor-selection flags each having 3 bits, a set of the80 (L+R)-related bit-number flags each having 5 bits, and a set of the80 (L−R)-related bit-number flags each having 5 bits. A set of the 80(L−R)-related bit-number flags is successively followed by a1-frame-corresponding set of the packing-resultant samples of theselected (L+R)-related prediction-error signal, and a1-frame-corresponding set of the packing-resultant samples of theselected (L−R)-related prediction-error signal. Since 80 sub-framescompose one frame and the number of bits of every packing-resultantsample varies from sub-frame to sub-frame, a 1-frame-corresponding setof the packing-resultant samples of the selected (L+R)-relatedprediction-error signal has a variable bit number. Also, a1-frame-corresponding set of the packing-resultant samples of theselected (L−R)-related prediction-error signal has a variable bitnumber.

The rate of compression of the variable-rate bit stream relative to thepair of the left-channel digital audio signal “L” and the right-channeldigital audio signal “R” is equal to, for example, 59%.

As shown in FIG. 4, the lossless decoder 3D includes a demultiplexer 21which receives the variable-rate bit stream from the transmission line250 (see FIG. 1). A first portion of the demultiplexer 21 detects everyframe header in the received variable-rate bit stream. For every frame,a second portion of the demultiplexer 21 demultiplexes, in response tothe detected frame header, the received variable-rate bit stream intothe first sample of the addition-result signal (L+R), the first sampleof the subtraction-result signal (L−R), a set of the 80 (L+R)-relatedpredictor-selection flags, a set of the 80 (L−R)-relatedpredictor-selection flags, a set of the 80 (L+R)-related bit-numberflags, a set of the 80 (L−R)-related bit-number flags, a1-frame-corresponding set of the packing-resultant samples of theselected (L+R)-related prediction-error signal, and a1-frame-corresponding set of the packing-resultant samples of theselected (L−R)-related prediction-error signal.

In the lossless decoder 3D, the demultiplexer 21 outputs the firstsample of the addition-result signal (L+R) to an accumulation circuit 25a for every frame. The demultiplexer 21 outputs the first sample of thesubtraction-result signal (L−R) to an accumulation circuit 25 b forevery frame. The demultiplexer 21 outputs every (L+R)-relatedpredictor-selection flag to predictors 24 a-1, 24 a-2, . . . , and 24a-n. The demultiplexer 21 outputs every (L−R)-relatedpredictor-selection flag to predictors 24 b-1, 24 b-2, . . . , and 24b-n. The demultiplexer 21 outputs every (L+R)-related bit-number flagand every (L−R)-related bit-number flag to a de-packing circuit 22. Thedemultiplexer 21 outputs every packing-resultant sample of the selected(L+R)-related prediction-error signal and every packing-resultant sampleof the selected (L−R)-related prediction-error signal to the de-packingcircuit 22.

For every sub-frame, the de-packing circuit 22 implements the unpackingof the packing-resultant samples of the selected (L+R)-relatedprediction-error signal in response to the (L+R)-related bit-numberflag. The de-packing circuit 22 outputs the resultant (L+R)-relatedprediction-error signal to an addition circuit 23 a. For everysub-frame, the de-packing circuit 22 implements the unpacking of thepacking-resultant samples of the selected (L−R)-related prediction-errorsignal in response to the (L−R)-related bit-number flag. The de-packingcircuit 22 outputs the resultant (L−R)-related prediction-error signalto an addition circuit 23 b.

The predictors 24 a-1, 24 a-2, . . . , and 24 a-n have the samecharacteristics as those of the predictors 12 a-1, 12 a-2, . . . , and12 a-n in the lossless encoder 2D, respectively. For every sub-frame,one of the predictors 24 a-1, 24 a-2, . . . , and 24 a-n is selected inresponse to the (L+R)-related predictor-selection flag. Specifically,one of the predictors 24 a-1, 24 a-2, . . . , and 24 a-n is selectedwhich has the same characteristic as the encoder-side predictor used forthe sub-frame of interest. The selected predictor generates aprediction-result signal in response to an output signal of the additioncircuit 23 a. The selected predictor is enabled to output theprediction-result signal to the addition circuit 23 a. The additioncircuit 23 a adds the (L+R)-related prediction-error signal and theprediction-result signal into the difference signal Δ(L+R) which isequal to the DPCM signal Δ(L+R) outputted from the differencecalculation circuit 11D1 in the lossless encoder 2D. The additioncircuit 23 a outputs the difference signal Δ(L+R) to the accumulationcircuit 25 a and the predictors 24 a-1, 24 a-2, . . . , and 24 a-n.

The predictors 24 b-1, 24 b-2, . . . , and 24 b-n have the samecharacteristics as those of the predictors 12 b-1, 12 b-2, . . . , and12 b-n in the lossless encoder 2D, respectively. For every sub-frame,one of the predictors 24 b-1, 24 b-2, . . . , and 24 b-n is selected inresponse to the (L−R)-related predictor-selection flag. Specifically,one of the predictors 24 b-1, 24 b-2, . . . , and 24 b-n is selectedwhich has the same characteristic as the encoder-side predictor used forthe sub-frame of interest. The selected predictor generates aprediction-result signal in response to an output signal of the additioncircuit 23 b. The selected predictor is enabled to output theprediction-result signal to the addition circuit 23 b. The additioncircuit 23 b adds the (L−R)-related prediction-error signal and theprediction-result signal into the difference signal Δ(L−R) which isequal to the DPCM signal Δ(L−R) outputted from the differencecalculation circuit 11D2 in the lossless encoder 2D. The additioncircuit 23 b outputs the difference signal Δ(L−R) to the accumulationcircuit 25 b and the predictors 24 b-1, 24 b-2, . . . , and 24 b-n.

The accumulation circuit 25 a accumulates samples of the differencesignal Δ(L+R) with respect to the first sample of the addition-resultsignal (L+R) in a frame, thereby reproducing a sequence of samples ofthe addition-result signal (L+R) which is equal to the output signal ofthe addition circuit 1 a in the channel correlation circuit “A” of theaudio signal encoding apparatus 100. The accumulation circuit 25 aoutputs the reproduced addition-result signal (L+R) to the channelcorrelation circuit “B” (see FIG. 1).

The accumulation circuit 25 b accumulates samples of the differencesignal Δ(L−R) with respect to the first sample of the subtraction-resultsignal (L−R) in a frame, thereby reproducing a sequence of samples ofthe subtraction-result signal (L−R) which is equal to the output signalof the subtraction circuit 1 b in the channel correlation circuit “A” ofthe audio signal encoding apparatus 100. The accumulation circuit 25 boutputs the reproduced subtraction-result signal (L−R) to the channelcorrelation circuit “B” (see FIG. 1).

With reference back to FIG. 1, the channel correlation circuit “B”includes an addition circuit 4 a, a subtraction circuit 4 b, and 1/2dividers 5 a and 5 b. The addition circuit 4 a receives theaddition-result signal (L+R) and the subtraction-result signal (L−R)from the lossless decoder 3D. The addition circuit 4 a adds theaddition-result signal (L+R) and the subtraction-result signal (L−R)into a signal 2L. The addition circuit 4 a outputs the signal 2L to thedivider 5 a. The divider 5 a halves the signal 2L, thereby reproducingthe original left-channel digital audio signal “L”. The divider 5 aoutputs the reproduced left-channel digital audio signal “L”. Thesubtraction circuit 4 b receives the addition-result signal (L+R) andthe subtraction-result signal (L−R) from the lossless decoder 3D. Thesubtraction circuit 4 b subtracts the subtraction-result signal (L−R)from the addition-result signal (L+R), thereby generating a signal 2R.The subtraction circuit 4 b outputs the signal 2R to the divider 5 b.The divider 5 b halves the signal 2R, thereby reproducing the originalright-channel digital audio signal “R”. The divider 5 b outputs thereproduced right-channel digital audio signal “R”.

SECOND EMBODIMENT

A second embodiment of this invention is similar to the first embodimentthereof except for design changes mentioned later.

FIG. 5 shows a lossless encoder in the second embodiment of thisinvention which is a modification of the lossless encoder 2D in thefirst embodiment of this invention.

The lossless encoder of FIG. 5 includes prediction circuits 15A and 15S,a buffer and selector 16A, and a buffer and selector 16S. The predictioncircuit 1SA is similar in structure to the prediction circuit 15D1. Theprediction circuit 15S is similar in structure to the prediction circuit15D2. The buffer and selector 16A is similar in structure to the bufferand selector 16D1. The buffer and selector 16S is similar in structureto the buffer and selector 16D2.

The prediction circuit 15A receives the PCM addition-result signal (L+R)from the buffer 10. The prediction circuit 15A generates a set of PCMprediction-error signals in response to the PCM addition-result signal(L+R). The prediction circuit 15A outputs the PCM prediction-errorsignals to the buffer and selector 16A. The PCM prediction-error signalsare temporarily stored in a memory within the buffer and selector 16A.The selection signal generator 17 outputs a selection signal to thebuffer and selector 16A. The selection signal is designed to select thesmallest one from among the PCM prediction-error signals in the memoryof the buffer and selector 16A as an output signal of an optimumsubtracter (an optimum predictor) for every sub-frame. Specifically, forevery sub-frame, the selection signal generator 17 searches the memorywithin the buffer and selector 16A for the smallest PCM prediction-errorsignal. The smallest PCM prediction-error signal is the selected PCM(L+R)-related prediction-error signal.

In addition, the selection signal generator 17 produces an (L+R)-relatedbit-number flag representing the maximum number among the numbers ofeffective bits in respective samples of the selected PCM (L+R)-relatedprediction-error signal which compose one sub-frame. For everysub-frame, the selection signal generator 17 outputs the (L+R)-relatedbit-number flag to the packing circuit 18 and the multiplexer 19. Also,for every sub-frame, the selection signal generator 17 produces an(L+R)-related predictor-selection flag representing the optimalpredictor causing the selected PCM (L+R)-related prediction-errorsignal. The selection signal generator 17 outputs the (L+R)-relatedpredictor-selection flag to the multiplexer 19.

The prediction circuit 15S receives the PCM subtraction-result signal(L−R) from the buffer 10. The prediction circuit 15S generates a set ofPCM prediction-error signals in response to the PCM subtraction-resultsignal (L−R). The prediction circuit 15S outputs the PCMprediction-error signals to the buffer and selector 16S. The PCMprediction-error signals are temporarily stored in a memory within thebuffer and selector 16S. The selection signal generator 17 outputs aselection signal to the buffer and selector 16S. The selection signal isdesigned to select the smallest one from among the PCM prediction-errorsignals in the memory of the buffer and selector 16S as an output signalof an optimum subtracter (an optimum predictor) for every sub-frame.Specifically, for every sub-frame, the selection signal generator 17searches the memory within the buffer and selector 16S for the smallestPCM prediction-error signal. The smallest PCM prediction-error signal isthe selected PCM (L−R)-related prediction-error signal.

In addition, the selection signal generator 17 produces an (L−R)-relatedbit-number flag representing the maximum number among the numbers ofeffective bits in respective samples of the selected PCM (L−R)-relatedprediction-error signal which compose one sub-frame. For everysub-frame, the selection signal generator 17 outputs the (L−R)-relatedbit-number flag to the packing circuit 18 and the multiplexer 19. Also,for every sub-frame, the selection signal generator 17 produces an(L−R)-related predictor-selection flag representing the optimalpredictor causing the selected PCM (L−R)-related prediction-errorsignal. The selection signal generator 17 outputs the (L−R)-relatedpredictor-selection flag to the multiplexer 19.

For every sub-frame, the selection signal generator 17 searches thememory within the buffer and selector 16D1 for the smallest DPCMprediction-error signal. The smallest DPCM prediction-error signal isthe selected DPCM (L+R)-related prediction-error signal. Also, for everysub-frame, the selection signal generator 17 searches the memory withinthe buffer and selector 16D2 for the smallest DPCM prediction-errorsignal. The smallest DPCM prediction-error signal is the selected DPCM(L−R)-related prediction-error signal. Furthermore, for every sub-frame,the selection signal generator 17 decides which of the pair of theselected PCM (L+R)-related prediction-error signal and the selected PCM(L−R)-related prediction-error signal, and the pair of the selected DPCM(L+R)-related prediction-error signal and the selected DPCM(L−R)-related prediction-error signal is higher in compression rate bycomparing the values represented thereby. The selection signal generator17 selects the higher-compression pair of the (L+R)-relatedprediction-error signal and the (L−R)-related prediction-error signal.The selection signal generator 17 enables the higher-compression pair ofthe (L+R)-related prediction-error signal and the (L−R)-relatedprediction-error signal to be outputted to the packing circuit 18.

For every sub-frame, the selection signal generator 17 produces aprediction-circuit-selection flag representing which of the PCMprediction-error signal pair and the DPCM prediction-error signal pairis selected. The selection signal generator 17 outputs theprediction-circuit-selection flag to the multiplexer 19. The multiplexer19 adds the prediction-circuit-selection flag into the variable-rate bitstream.

FIG. 6 shows a lossless decoder in the second embodiment of thisinvention which is a modification of the lossless decoder 3D in thefirst embodiment of this invention. The lossless decoder of FIG. 6includes selectors 26 a and 26 b. The demultiplexer 21 separates everyprediction-circuit-selection flag from the variable-rate bit stream. Thedemultiplexer 21 feeds the prediction-circuit-selection flag to theselectors 26 a and 26 b. When the prediction-circuit-selection flagindicates that the DPCM prediction-error signal pair is selected, theselector 26 a selects the output signal of the accumulation circuit 25 aand the selector 26 b selects the output signal of the accumulationcircuit 25 b. When the prediction-circuit-selection flag indicates thatthe PCM prediction-error signal pair is selected, the selector 26 aselects the output signal of the addition circuit 23 a and the selector26 b selects the output signal of the addition circuit 23 b. The signalselected by the selector 26 a constitutes the reproduced addition-resultsignal (L+R). The signal selected by the selector 26 b constitutes thereproduced subtraction-result signal (L−R).

THIRD EMBODIMENT

A third embodiment of this invention is similar to the first embodimentthereof except for design changes mentioned later. FIG. 7 shows an audiosignal encoding apparatus in the third embodiment of this inventionwhich is a modification of the audio signal encoding apparatus 100 inthe first embodiment of this invention.

The audio signal encoding apparatus of FIG. 7 includes a buffer 10 inwhich a left-channel digital audio signal “L” and a right-channeldigital audio signal “R” are temporarily stored. The left-channeldigital audio signal “L” is fed from the buffer 10 to a predictioncircuit 15L and a channel correlation circuit “A”. The right-channeldigital audio signal “R” is fed from the buffer 10 to a predictioncircuit 15R and the channel correlation circuit “A”. For every frame,the first sample of the left-channel digital audio signal “L” and thefirst sample of the right-channel digital audio signal “R” aretransmitted from the buffer 10 to the multiplexer 19.

An addition circuit 1 a in the channel correlation circuit “A” adds theleft-channel digital audio signal “L” and the right-channel digitalaudio signal “R” into a PCM addition-result signal (L+R). The additioncircuit 1 a outputs the PCM addition-result signal (L+R) to a predictioncircuit 15A and a difference calculation circuit 11D1. For every frame,the first sample of the PCM addition-result signal (L+R) is transmittedfrom the addition circuit 1 a to the multiplexer 19. A subtractioncircuit 1 b in the channel correlation circuit “A” subtracts theright-channel digital audio signal “R” from the left-channel digitalaudio signal “L”, thereby generating a PCM subtraction-result signal(L−R). The subtraction circuit 1 b outputs the PCM subtraction-resultsignal (L−R) to a prediction circuit 15S and a difference calculationcircuit 11D2. For every frame, the first sample of the PCMsubtraction-result signal (L−R) is transmitted from the subtractioncircuit 1 b to the multiplexer 19.

The difference calculation circuit 11D1 generates a DPCM signal Δ(L+R)from the PCM addition-result signal (L+R). The difference calculationcircuit 11D1 outputs the DPCM signal Δ(L+R) to a prediction circuit15D1. The difference calculation circuit 11D2 generates a DPCM signalΔ(L−R) from the PCM subtraction-result signal (L−R). The differencecalculation circuit 11D2 outputs the DPCM signal Δ(L−R) to a predictioncircuit 15D2.

The prediction circuits 15A and 15L are similar in structure to theprediction circuit 15D1. The prediction circuits 15R and 15S are similarin structure to the prediction circuit 15D2. The prediction circuit 15Ais followed by a buffer and selector 16A. The prediction circuit 15L isfollowed by a buffer and selector 16L. The prediction circuit 15R isfollowed by a buffer and selector 16R. The prediction circuit 15S isfollowed by a buffer and selector 16S. The prediction circuit 15D1 isfollowed by a buffer and selector 16D1. the prediction circuit 15D2 isfollowed by a buffer and selector 16D2. The buffer and selector 16A issimilar in structure to the buffer and selector 16D1. The buffer andselector 16L is similar in structure to the buffer and selector 16D1.The buffer and selector 16R is similar in structure to the buffer andselector 16D2. The buffer and selector 16S is similar in structure tothe buffer and selector 16D2.

The prediction circuit 15A receives the PCM addition-result signal (L+R)from the addition circuit 1 a in the channel correlation circuit “A”.The prediction circuit 15A generates a set of PCM prediction-errorsignals in response to the PCM addition-result signal (L+R). Theprediction circuit 15A outputs the PCM prediction-error signals to thebuffer and selector 16A. The PCM prediction-error signals aretemporarily stored in a memory within the buffer and selector 16A. Theselection signal generator 17 outputs a selection signal to the bufferand selector 16A. The selection signal is designed to select thesmallest one from among the PCM prediction-error signals in the memoryof the buffer and selector 16A as an output signal of an optimumsubtracter (an optimum predictor) for every sub-frame. Specifically, forevery sub-frame, the selection signal generator 17 searches the memorywithin the buffer and selector 16A for the smallest PCM prediction-errorsignal. The smallest PCM prediction-error signal is the selected PCM(L+R)-related prediction-error signal.

In addition, the selection signal generator 17 produces an (L+R)-relatedbit-number flag representing the maximum number among the numbers ofeffective bits in respective samples of the selected PCM (L+R)-relatedprediction-error signal which compose one sub-frame. For everysub-frame, the selection signal generator 17 outputs the (L+R)-relatedbit-number flag to the packing circuit 18 and the multiplexer 19. Also,for every sub-frame, the selection signal generator 17 produces an(L+R)-related predictor-selection flag representing the optimalpredictor causing the selected PCM (L+R)-related prediction-errorsignal. The selection signal generator 17 outputs the (L+R)-relatedpredictor-selection flag to the multiplexer 19.

The prediction circuit 15S receives the PCM subtraction-result signal(L−R) from the subtraction circuit 1 b in the channel correlationcircuit “A”. The prediction circuit 15S generates a set of PCMprediction-error signals in response to the PCM subtraction-resultsignal (L−R). The prediction circuit 15S outputs the PCMprediction-error signals to the buffer and selector 16S. The PCMprediction-error signals are temporarily stored in a memory within thebuffer and selector 16S. The selection signal generator 17 outputs aselection signal to the buffer and selector 16S. The selection signal isdesigned to select the smallest one from among the PCM prediction-errorsignals in the memory of the buffer and selector 16S as an output signalof an optimum subtracter (an optimum predictor) for every sub-frame.Specifically, for every sub-frame, the selection signal generator 17searches the memory within the buffer and selector 16S for the smallestPCM prediction-error signal. The smallest PCM prediction-error signal isthe selected PCM (L−R)-related prediction-error signal.

In addition, the selection signal generator 17 produces an (L−R)-relatedbit-number flag representing the maximum number among the numbers ofeffective bits in respective samples of the selected PCM (L−R)-relatedprediction-error signal which compose one sub-frame. For everysub-frame, the selection signal generator 17 outputs the (L−R)-relatedbit-number flag to the packing circuit 18 and the multiplexer 19. Also,for every sub-frame, the selection signal generator 17 produces an(L−R)-related predictor-selection flag representing the optimalpredictor causing the selected PCM (L−R)-related prediction-errorsignal. The selection signal generator 17 outputs the (L−R)-relatedpredictor-selection flag to the multiplexer 19.

The prediction circuit 15L receives the left-channel digital audiosignal “L” from the buffer 10. The prediction circuit 15L generates aset of original-L prediction-error signals in response to theleft-channel digital audio signal “L”. The prediction circuit 15Loutputs the original-L prediction-error signals to the buffer andselector 16L. The original-L prediction-error signals are temporarilystored in a memory within the buffer and selector 16L.

The selection signal generator 17 outputs a selection signal to thebuffer and selector 16L. The selection signal is designed to select thesmallest one from among the original-L prediction-error signals in thememory of the buffer and selector 16L as an output signal of an optimumsubtracter (an optimum predictor) for every sub-frame. Specifically, forevery sub-frame, the selection signal generator 17 searches the memorywithin the buffer and selector 16L for the smallest original-Lprediction-error signal. The smallest original-L prediction-error signalis the selected original-L prediction-error signal.

In addition, the selection signal generator 17 produces an L-relatedbit-number flag representing the maximum number among the numbers ofeffective bits in respective samples of the selected original-Lprediction-error signal which compose one sub-frame. For everysub-frame, the selection signal generator 17 outputs the L-relatedbit-number flag to the packing circuit 18 and the multiplexer 19. Also,for every sub-frame, the selection signal generator 17 produces anL-related predictor-selection flag representing the optimal predictorcausing the selected original-L prediction-error signal. The selectionsignal generator 17 outputs the L-related predictor-selection flag tothe multiplexer 19.

The prediction circuit 15R receives the right-channel digital audiosignal “R” from the buffer 10. The prediction circuit 15R generates aset of original-R prediction-error signals in response to theright-channel digital audio signal “R”. The prediction circuit 15Routputs the original-R prediction-error signals to the buffer andselector 16R. The original-R prediction-error signals are temporarilystored in a memory within the buffer and selector 16R. The selectionsignal generator 17 outputs a selection signal to the buffer andselector 16R. The selection signal is designed to select the smallestone from among the original-R prediction-error signals in the memory ofthe buffer and selector 16R as an output signal of an optimum subtracter(an optimum predictor) for every sub-frame. Specifically, for everysub-frame, the selection signal generator 17 searches the memory withinthe buffer and selector 16R for the smallest original-R prediction-errorsignal. The smallest original-R prediction-error signal is the selectedoriginal-R prediction-error signal.

In addition, the selection signal generator 17 produces an R-relatedbit-number flag representing the maximum number among the numbers ofeffective bits in respective samples of the selected original-Rprediction-error signal which compose one sub-frame. For everysub-frame, the selection signal generator 17 outputs the R-relatedbit-number flag to the packing circuit 18 and the multiplexer 19. Also,for every sub-frame, the selection signal generator 17 produces anR-related predictor-selection flag representing the optimal predictorcausing the selected original-R prediction-error signal. The selectionsignal generator 17 outputs the R-related predictor-selection flag tothe multiplexer 19.

For every sub-frame, the selection signal generator 17 searches thememory within the buffer and selector 16D1 for the smallest DPCMprediction-error signal. The smallest DPCM prediction-error signal isthe selected DPCM (L+R)-related prediction-error signal. Also, for everysub-frame, the selection signal generator 17 searches the memory withinthe buffer and selector 16D2 for the smallest DPCM prediction-errorsignal. The smallest DPCM prediction-error signal is the selected DPCM(L−R)-related prediction-error signal.

Furthermore, for every sub-frame, the selection signal generator 17decides which of the pair of the original-L prediction-error signal andthe original-R prediction-error signal, the pair of the selected PCM(L+R)-related prediction-error signal and the selected PCM (L−R)-relatedprediction-error signal, and the pair of the selected DPCM (L+R)-relatedprediction-error signal and the selected DPCM (L−R)-relatedprediction-error signal is the highest in compression rate by comparingthe values represented thereby. The selection signal generator 17selects the highest-compression pair of the prediction-error signals.The selection signal generator 17 enables the highest-compression pairof the prediction-error signals to be outputted to the packing circuit18.

For every sub-frame, the selection signal generator 17 produces aprediction-circuit-selection flag representing which of the originalprediction-error signal pair, the PCM prediction-error signal pair, andthe DPCM prediction-error signal pair is selected. The selection signalgenerator 17 outputs the prediction-circuit-selection flag to themultiplexer 19. The multiplexer 19 adds the prediction-circuit-selectionflag into the variable-rate bit stream.

FIG. 8 shows an audio signal decoding apparatus in the third embodimentof this invention which is a modification of the audio signal decodingapparatus 200 in the first embodiment of this invention. The audiosignal decoding apparatus of FIG. 8 includes selectors 26 a, 26 b, 27 a,and 27 b. The demultiplexer 21 separates everyprediction-circuit-selection flag from the variable-rate bit stream. Thedemultiplexer 21 feeds the prediction-circuit-selection flag to theselectors 26 a, 26 b, 27 a, and 27 b. When theprediction-circuit-selection flag indicates that the DPCMprediction-error signal pair is selected, the selector 26 a selects theoutput signal of the accumulation circuit 25 a and the selector 26 bselects the output signal of the accumulation circuit 25 b. When theprediction-circuit-selection flag indicates that the PCMprediction-error signal pair is selected, the selector 26 a selects theoutput signal of the addition circuit 23 a and the selector 26 b selectsthe output signal of the addition circuit 23 b. The signal selected bythe selector 26 a constitutes the reproduced addition-result signal(L+R). The signal selected by the selector 26 b constitutes thereproduced subtraction-result signal (L−R). The reproducedaddition-result signal (L+R) and the reproduced subtraction-resultsignal (L−R) are fed to the channel correlation circuit “B”.

When the prediction-circuit-selection flag indicates that the originalprediction-error signal pair is selected, the selector 27 a selects theoutput signal of the addition circuit 23 a and the selector 27 b selectsthe output signal of the addition circuit 23 b. Otherwise, the selector27 a selects the output signal of the divider 5 a in the channelcorrelation circuit “B” and the selector 27 b selects the output signalof the divider 5 b in the channel correlation circuit “B”. The signalselected by the selector 27 a constitutes the reproduced left-channeldigital audio signal “L”. The signal selected by the selector 27 bconstitutes the reproduced right-channel digital audio signal “R”.

FOURTH EMBODIMENT

A fourth embodiment of this invention is similar to one of the first,second, and third embodiments thereof except for design changesmentioned later.

With reference to FIG. 9, the fourth embodiment of this inventionincludes a DVD-audio encoder 300 which follows the audio signal encodingapparatus 100. The DVD-audio encoder 300 converts the output signal ofthe audio signal encoding apparatus (that is, the variable-rate bitstream) into a DVD-audio-format signal.

The DVD-audio encoder 300 outputs the DVD-audio-format signal to a DVDdrive 302. A writer in the DVD drive 302 records the DVD-audio-formatsignal on a DVD-audio disc 304.

A reader in the DVD drive 302 reproduces the DVD-audio-format signalfrom the DVD-audio disc 304. The reader in the DVD drive 302 outputs thereproduced signal to a DVD-audio decoder 306. The DVD-audio decoder 306recovers the variable-rate bit stream from the reproduced signal. TheDVD-audio decoder 306 outputs the recovered variable-rate bit stream tothe audio signal decoding apparatus 200.

The DVD-audio-format signal generated by the DVD-audio encoder 300 has astream of packs including audio packs. As shown in FIG. 10, each audiopack has a sequence of 4-byte pack start information, 6-byte SCR (systemclock reference) information, 3-byte mux rate information, 1-bytestuffing data, and 2,034-byte packet-form user data. Thus, each audiopack has 2,048 bytes. In each audio pack, pack start information, SCRinformation, mux rate information, and stuffing data compose a 14-bytepack header. SCR information in each audio pack serves as a time stamp.In each audio pack, 2,034-byte packet-form user data contains a portionof the variable-rate bit stream.

A time stamp in a first audio pack among audio packs related to onetitle is set to “1”. Time stamps in second and later audio packs relatedto the same title are set to serial numbers “2”, “3”, “4”, . . . ,respectively. The serially-numbered time stamps make it possible tomanage times of audio packs related to the same title.

As shown in FIG. 11, one audio pack has a 14-byte pack header and anaudio packet. The pack header is followed by the audio packet. The audiopacket has a sequence of a packet header, a private header, and audiodata (linear PCM audio data). The packet header has 9 bytes, 14 bytes,or 17 bytes. The audio data has 1 byte to 2,011 bytes. The audio data isa portion of the variable-rate bit stream.

As shown in FIG. 11, the private header has a sequence of 1-byte substream ID (identification) information, 2-byte information of anUPC/EAN-ISRC (Universal Product Code/European ArticleNumber-International Standard Recording Code) number and UPC/EAN-ISRCdata, 1-byte information of the private header length, a 2-byte firstaccess unit pointer, 8-byte audio data information ADI, and 0 to 7stuffing bytes.

FIFTH EMBODIMENT

A fifth embodiment of this invention is similar to one of the first,second, and third embodiments thereof except for design changesmentioned later.

With reference to FIG. 12, the fifth embodiment of this inventionincludes a packeting processor 350 which follows the audio signalencoding apparatus 100. The packeting processor 350 encodes the outputsignal of the audio signal encoding apparatus (that is, thevariable-rate bit stream) into a packet stream. The packeting processor350 transmits the packet stream to a communication network (or acommunication line) 360.

A de-packeting processor 370 receives the packet stream from thecommunication network 360. The de-packeting processor 370 decodes thepacket stream into the variable-rate bit stream. The de-packetingprocessor 370 outputs the variable-rate bit stream to the audio signaldecoding apparatus 200.

The packeting processor 350 operates in accordance with a controlprogram stored in its internal ROM or another memory. FIG. 13 is aflowchart of a segment of the control program. As shown in FIG. 13, afirst step S41 of the program segment divides the variable-rate bitstream into basic packets each having a predetermined number of bits. Astep S42 following the step S41 adds headers to the starting ends of thebasic packets to change the basic packets to final packets respectively.Generally, the added headers include destination addresses. A step S43subsequent to the step S42 sequentially transmits the final packets tothe communication network 360.

The de-packeting processor 370 operates in accordance with a controlprogram stored in its internal ROM or another memory. FIG. 14 is aflowchart of a segment of the control program. As shown in FIG. 14, afirst step S51 of the program segment removes headers from receivedpackets. A step S52 following the step S51 recovers the variable-ratebit stream from the header-less packets. A step S53 subsequent to thestep S52 stores the recovered variable-rate bit stream into a buffermemory provided in the de-packeting processor 370. The variable-rate bitstream is transmitted from the buffer memory to the audio signaldecoding apparatus 200.

SIXTH EMBODIMENT

FIG. 15 shows a sixth embodiment of this invention which is similar tothe first embodiment thereof except for design changes indicatedhereinafter.

The embodiment of FIG. 15 includes a lossless encoder 2E and a losslessdecoder 3E which replace the lossless encoder 2D and the losslessdecoder 3D (see FIG. 1) respectively. The lossless encoder 2E follows achannel correlation circuit “A”. The lossless decoder 3E precedes achannel correlation circuit “B”.

The embodiment of FIG. 15 includes a channel correlation circuits A2 andB2. The channel correlation circuit A2 precedes the lossless encoder 2E.The channel correlation circuit B2 follows the lossless decoder 3E.

An encoder side of the embodiment of FIG. 15 receives a multi-channeldigital audio signal composed of a left-channel digital audio signal“L”, a right-channel digital audio signal “R”, a left surround signal“SL”, and a right surround signal “SR”. The multi-channel digital audiosignal is reproduced from a digital recording medium such as a DVD-audio(a digital versatile disc audio). The left-channel digital audio signal“L” and the right-channel digital audio signal “R” are processed by thechannel correlation circuit “A” into an addition-result signal (L+R) anda subtraction-result signal (L−R). The addition-result signal (L+R) andthe subtraction-result signal (L−R) are fed to the lossless encoder 2E.The left surround signal “SL” and the right surround signal “SR” areprocessed by the channel correlation circuit A2 into an addition-resultsignal (SL+SR) and a subtraction-result signal (SL−SR). Theaddition-result signal (SL+SR) and the subtraction-result signal (SL−SR)are fed to the lossless encoder 2E.

The channel correlation circuit A2 includes an addition circuit 1 a 2and a subtraction circuit 1 b 2. The addition circuit 1 a 2 receives theleft surround signal “SL” and the right surround signal “SR”. Theaddition circuit 1 a 2 adds the left surround signal “SL” and the rightsurround signal “SR” into an addition-result signal (SL+SR). Theaddition circuit 1 a 2 outputs the addition-result signal (SL+SR) to thelossless encoder 2E. The subtraction circuit 1 b 2 receives the leftsurround signal “SL” and the right surround signal “SR”. The subtractioncircuit 1 b 2 subtracts the right surround signal “SR” from the leftsurround signal “SL”, thereby generating a subtraction-result signal(SL−SR). The subtraction circuit 1 b 2 outputs the subtraction-resultsignal (SL−SR) to the lossless encoder 2E.

The lossless encoder 2E encodes the addition-result signal (L+R) and thesubtraction-result signal (L−R) into a first encoding-resultant signalas the lossless encoder 2D in FIG. 1 does. Similarly, the losslessencoder 2E encodes the addition-result signal (SL+SR) and thesubtraction-result signal (SL−SR) into a second encoding-resultantsignal. The lossless encoder 2E combines the first encoding-resultantsignal and the second encoding-resultant signal into a variable-rate bitstream representing a sequence of variable-bit-number frames. Thelossless encoder 2E outputs the variable-rate bit stream to atransmission line 250.

FIG. 16 shows the format of every frame of the variable-rate bit streamoutputted from the lossless encoder 2E. As shown in FIG. 16, a startingportion of every frame has a frame header. The frame header issuccessively followed by a first data section and a second data section.The first data section is loaded with information related to theaddition-result signal (L+R) and the subtraction-result signal (L−R).The second data section is loaded with information related to theaddition-result signal (SL+SR) and the subtraction-result signal(SL−SR).

With reference back to FIG. 15, the lossless decoder 3E receives thevariable-rate bit stream from the transmission line 250. The losslessdecoder 3E divides the variable-rate bit stream into first informationrelated to the addition-result signal (L+R) and the subtraction-resultsignal (L−R), and second information related to the addition-resultsignal (SL+SR) and the subtraction-result signal (SL−SR). The losslessdecoder 3E decodes the first information into the addition-result signal(L+R) and the subtraction-result signal (L−R) as the lossless decoder 3Din FIG. 1 does. The lossless decoder 3E outputs the addition-resultsignal (L+R) and the subtraction-result signal (L−R) to the channelcorrelation circuit “B”. Similarly, the lossless decoder 3E decodes thesecond information into the addition-result signal (SL+SR) and thesubtraction-result signal (SL−SR). The lossless decoder 3E outputs theaddition-result signal (SL+SR) and the subtraction-result signal (SL−SR)to the channel correlation circuit B2.

The channel correlation circuit B includes an addition circuit 4 a 2, asubtraction circuit 4 b 2, and 1/2 dividers 5 a 2 and 5 b 2. Theaddition circuit 4 a 2 receives the addition-result signal (SL+SR) andthe subtraction-result signal (SL−SR) from the lossless decoder 3E. Theaddition circuit 4 a 2 adds the addition-result signal (SL+SR) and thesubtraction-result signal (SL−SR) into a signal 2SL. The additioncircuit 4 a 2 outputs the signal 2SL to the divider 5 a 2. The divider 5a 2 halves the signal 2SL, thereby reproducing the original leftsurround signal “SL”. The divider 5 a 2 outputs the reproduced leftsurround signal “SL”. The subtraction circuit 4 b 2 receives theaddition-result signal (SL+SR) and the subtraction-result signal (SL−SR)from the lossless decoder 3E. The subtraction circuit 4 b 2 subtractsthe subtraction-result signal (SL−SR) from the addition-result signal(SL+SR), thereby generating a signal 2SR. The subtraction circuit 4 b 2outputs the signal 2SR to the divider 5 b 2. The divider 5 b 2 halvesthe signal 2SR, thereby reproducing the original right surround signal“SR”. The divider 5 b 2 outputs the reproduced right surround signal“SR”.

SEVENTH EMBODIMENT

FIG. 17 shows a seventh embodiment of this invention which is similar tothe first embodiment thereof except for design changes indicatedhereinafter.

The embodiment of FIG. 17 includes a lossless encoder 2F and a losslessdecoder 3F which replace the lossless encoder 2D and the loss decoder 3D(see FIG. 1) respectively. The lossless encoder 2F follows a channelcorrelation circuit “A”. The lossless decoder 3F precedes a channelcorrelation circuit “B”.

An encoder side of the embodiment of FIG. 17 receives a multi-channeldigital audio signal composed of a left-channel digital audio signal“L”, a right-channel digital audio signal “R”, a center signal “C”, aleft surround signal “SL”, a right surround signal “SR”, and a lowfrequency effect signal “LFE”. The multi-channel digital audio signal isreproduced from a digital recording medium such as a DVD-audio (adigital versatile disc audio). The left-channel digital audio signal “L”and the right-channel digital audio signal “R” are processed by thechannel correlation circuit “A” into an addition-result signal (L+R) anda subtraction-result signal (L−R). The addition-result signal (L+R) andthe subtraction-result signal (L−R) are fed to the lossless encoder 2F.The center signal “C”, the left surround signal “SL”, the right surroundsignal “SR”, and the low frequency effect signal “LFE” are directlyapplied to the lossless encoder 2F.

The lossless encoder 2E encodes the addition-result signal (L+R) and thesubtraction-result signal (L−R) into a first encoding-resultant signalas the lossless encoder 2D in FIG. 1 does. Also, the lossless encoder 2Fencodes the center signal “C”, the left surround signal “SL”, the rightsurround signal “SR”, and the low frequency effect signal “LFE” intosecond, third, fourth, and fifth encoding-resultant signals,respectively. The lossless encoder 2F combines the first, second, third,fourth, and fifth encoding-resultant signals into a variable-rate bitstream representing a sequence of variable-bit-number frames. Thelossless encoder 2F outputs the variable-rate bit stream to atransmission line 250.

FIG. 18 shows the format of every frame of the variable-rate bit streamoutputted from the lossless encoder 2F. As shown in FIG. 18, a startingportion of every frame has a frame header. The frame header issuccessively followed by a first data section and a second data section.The first data section is loaded with information related to theaddition-result signal (L+R) and the subtraction-result signal (L−R).The second data section is loaded with information related to the centersignal “C”, the left surround signal “SL”, the right surround signal“SR”, and the low frequency effect signal “LFE”.

With reference back to FIG. 17, the lossless decoder 3F receives thevariable-rate bit stream from the transmission line 250. The losslessdecoder 3F divides the variable-rate bit stream into first informationrelated to the addition-result signal (L+R) and the subtraction-resultsignal (L−R), and second information related to the center signal “C”,the left surround signal “SL”, the right surround signal “SR”, and thelow frequency effect signal “LFE”. The lossless decoder 3F decodes thefirst information into the addition-result signal (L+R) and thesubtraction-result signal (L−R) as the lossless decoder 3D in FIG. 1does. The lossless decoder 3F outputs the addition-result signal (L+R)and the subtraction-result signal (L−R) to the channel correlationcircuit “B”. Similarly, the lossless decoder 3F decodes the secondinformation into the center signal “C”, the left surround signal “SL”,the right surround signal “SR”, and the low frequency effect signal“LFE”. The lossless decoder 3F outputs the center signal “C”, the leftsurround signal “SL”, the right surround signal “SR”, and the lowfrequency effect signal “LFE”.

EIGHTH EMBODIMENT

FIG. 19 shows an eighth embodiment of this invention which is similar tothe first embodiment thereof except for design changes indicatedhereinafter.

The embodiment of FIG. 19 includes channel correlation circuits A3 andB3 which replace the channel correlation circuits “A” and “B” (seeFIG. 1) respectively. The channel correlation circuit A3 includes a 1/2divider 5 a 3 connected between an addition circuit 1 a and a losslessencoder 2D. Also, the channel correlation circuit A3 includes a 1/2divider 5 b 3 connected between a subtraction circuit 1 b and thelossless encoder 2D. The 1/2 dividers 5 a and 5 b (see FIG. 1) areremoved from the channel correlation circuit B3.

NINTH EMBODIMENT

FIG. 20 shows a ninth embodiment of this invention which is similar tothe seventh embodiment thereof except for design changes indicatedhereinafter.

The embodiment of FIG. 20 includes channel correlation circuits A3 andB3 which replace the channel correlation circuits “A” and “B” (see FIG.17) respectively. The channel correlation circuit A3 includes a 1/2divider 5 a 3 connected between an addition circuit 1 a and a losslessencoder 2F. Also, the channel correlation circuit A3 includes a 1/2divider 5 b 3 connected between a subtraction circuit 1 b and thelossless encoder 2F. On the other hand, 1/2 dividers 5 a and 5 b (seeFIG. 17) are removed from the channel correlation circuit B3.

1. An audio signal-recording disc encoded by a method which comprisesthe steps of: implementing matrix operation between a first audio signaland a second audio signal to generate a first channel signal and asecond channel signal correlating with each other, the first audiosignal and the second audio signal relating to a same samplingfrequency; subjecting the first channel signal and the second channelsignal to lossless encoding to convert the first channel signal and thesecond channel signal into an encoding-resultant signal from which adecoding side can reproduce the first audio signal and the second audiosignal; wherein the subjecting step comprises: 1) selecting a firstsample among samples of the first channel signal for every prescribedinterval of frame; 2) selecting a first sample among samples of thesecond channel signal for every prescribed interval of frame; 3)selecting one from first different linear prediction methods andpredictively encoding the first channel signal according to the selectedone of the first different linear prediction methods, wherein the firstdifferent linear prediction methods are of predicting the first channelsignal from a past condition of the first channel signal for everyprescribed interval of subframe which is a subdivision of the frame togenerate first different prediction signals for the first channelsignal, and generating first prediction-error signals representingdifferences between the first channel signal and the first differentprediction signals respectively, and wherein the selected first linearprediction method generates a smallest of the first prediction-errorsignals; 4) selecting one from second different linear predictionmethods and predictively encoding the second channel signal according tothe selected one of the second different linear prediction methods,wherein the second different linear prediction methods are of predictingthe second channel signal from a past condition of the second channelsignal for every prescribed interval of the subframe to generate seconddifferent prediction signals for the second channel signal, andgenerating second prediction-error signals representing differencesbetween the second channel signal and the second different predictionsignals respectively, and wherein the selected second linear predictionmethod generates a smallest of the second prediction-error signals; and5) generating a signal of a predetermined format having a headerinformation area and a user data area, and loading the user data areawith the selected first sample of the first channel signal, the selectedfirst sample of the second channel signal, the smallest firstprediction-error signal generated by the selected first linearprediction method, the smallest second prediction-error signal generatedby the selected second linear prediction method, an information piecerepresenting the selected first linear prediction method, and aninformation piece representing the selected second linear predictionmethod.
 2. A method of recording data to or reproducing data from theaudio signal recording disc according to claim
 1. 3. A method ofnetwork-based communication, comprising the steps of: transmitting andreceiving a signal of a predetermined transmission packet format to andfrom a communication line, wherein the signal has been generated by anaudio signal encoding method comprising: implementing matrix operationbetween a first audio signal and a second audio signal to generate afirst channel signal and a second channel signal correlating with eachother, the first audio signal and the second audio signal relating to asame sampling frequency; subjecting the first channel signal and thesecond channel signal to lossless encoding to convert the first channelsignal and the second channel signal into an encoding-resultant signalfrom which a decoding side can reproduce the first audio signal and thesecond audio signal: wherein the subjecting step comprises: 1) selectinga first sample among samples of the first channel signal for everyprescribed interval of frame; 2) selecting a first sample among samplesof the second channel signal for every prescribed interval of frame; 3)selecting one from first different linear prediction methods andpredictively encoding the first channel signal according to the selectedone of the first different linear prediction methods, wherein the firstdifferent linear prediction methods are of predicting the first channelsignal from a past condition of the first channel signal for everyprescribed interval of subframe which is a subdivision of the frame togenerate first different prediction signals for the first channelsignal, and generating first prediction-error signals representingdifferences between the first channel signal and the first differentprediction signals respectively, and wherein the first linear predictionmethod selected generates a smallest of the first prediction-errorsignals; 4) selecting one from second different linear predictionmethods and predictively encoding the second channel signal according tothe selected one of the second different linear prediction methods,wherein the second different linear prediction methods are of predictingthe second channel signal from a past condition of the second channelsignal for every prescribed interval of the subframe to generate seconddifferent prediction signals for the second channel signal, andgenerating second prediction-error signals representing differencesbetween the second channel signal and the second different predictionsignals respectively, and wherein the selected second linear predictionmethod generates a smallest of the second prediction-error signals; and5) generating a signal of a predetermined format having a headerinformation area and a user data area, and loading the user data areawith the selected first sample of the first channel signal, the selectedfirst sample of the second channel signal, the smallest firstprediction-error signal generated by the selected first linearprediction method, the smallest second prediction-error signal generatedby the selected second linear prediction method, an information piecerepresenting the selected first linear prediction method and aninformation piece representing the selected second linear predictionmethod.
 4. A method of reproducing data which is provided via thenetwork-based communication according to claim 3.